Polyamides & Poly(ethenol) (Edexcel International A Level Chemistry): Revision Note

Polyamides - Physical Properties

Examples of polyamides

Kevlar

• Kevlar is an example of a polymer formed through condensation polymerisation

• The polymer chains are neatly arranged with many hydrogen bonds between them

• This results in a strong and flexible polymer material with fire resistance properties

• These properties also lend Kevlar to a vital application in bullet-proof vests

• The monomers used to make Kevlar are:

  • 1,4-diaminobenzene

  • Benzene-1,4-dicarboxylic acid

• As seen with Nylon, a dioyl dichloride can be used instead of the acid as well (benzene-1,4-dioyl chloride)

Kevlar is made using a diamine and dicarboxylic acid monomers

Nylon 6-6

• Nylon 6,6 is a synthetic polyamide

• Its monomers are 1,6-diaminohexane and hexane-1,6-dioic acid

  • The ‘6,6’ part of its name arises from the 6 carbon atoms in each of Nylon 6,6 monomers

Nylon 6,6 is a synthetic polyamide made using diamine and dicarboxylic acid monomers

Properties of polyamides

• Most polyamides (nylons) tend to be semi-crystalline

• They are generally very tough with good thermal and chemical resistance

• Polyamides tend to absorb moisture from their surroundings

  • This absorption increases until equilibrium is reached

• The impact resistance and flexibility of polyamides increases with water content whilst strength and stiffness decrease

• The strong bonds in polyamides make the polyamide chains strong allowing them to be made into strong fibres for clothing

  • E.g. Kevlar shown above

• Polyamide film (cling film) is used in food packaging due to its toughness and the fact it prevents gas molecules from passing through

• Polyamide film is also used for 'Boil in the bag' foods due to its high-temperature resistance

Poly(ethenol)

• Poly(ethenol) is another addition polymer, sometimes called poly(vinyl alcohol)

• It is not made in the usual way by directly polymerising a monomer

• Instead, it is made in two stages:

Stage 1: polymerisation of ethenyl ethanoate

Stage 2: poly(ethenyl ethanoate) reacts with methanol forming poly(ethenol) and methyl ethanoate (this process is known as ester exchange)

• The amount of ester exchange is controlled by varying the temperature

Solubility

• Poly(ethenol) contains many OH groups

• These groups can form hydrogen bonds with water making poly(ethenol) soluble in water

• The degree of solubility depends on how many ester groups have been replaced with OH groups

  • Solubility ranges from insoluble, to soluble in warm/hot water, to soluble in cold water

Uses

• Poly(ethenol) is used to make disposable laundry bags for use in hospitals

  • These laundry bags are soluble in water

• Dirty bedding and clothing, which may be covered in microorganisms from patients, are put in the laundry bags

• The bag is then placed in the washing machine without hospital workers having to touch the dirty fabrics

• During washing the bag dissolves and the fabrics are washed clean

• Poly(ethenol) is also used to make liquid-detergent capsules that contain measured quantities of detergent for use in washing machine and dishwashers

  • The capsule dissolves during use